At present, different types of fibers are used to reinforce concretes and mortars. The fibers can provide the concrete with different properties, such as reducing cracking, improving passive resistance against fire, etc., even though the fundamental difference is the structural capacity thereof, that is to say, whether the fibers have structural character at the time of providing the concrete/mortar with mechanical features. Even though until a few years ago the only possibility of structurally reinforcing the concretes and the mortars with fibers was the use of metallic fibers, the advances in polymers have allowed for some types of synthetic fibers to be able to be considered structural fibers and, taken into account in the calculations for such purpose. In Spain, the legislation in force (EHE-80) makes reference to this differentiation, distinguishing the structural character thereof with the terms macro-fibers and micro-fibers.
Among the macro-synthetic fibers, those with a polyolefin base (polypropylene, polyethylene, etc.) are the most used, both for the competitive price thereof and for the features thereof. The improvement of the fibrillation by means of the use of mineral loads, etc., is known in the state of the art for improving different properties of the fibers, such as the adherence between the fiber and the concrete/mortar.
However, although these types of fibers have a resistance to traction in many cases greater than that of the steel itself used for reinforcing the concretes/mortars, the elastic modulus thereof is low, since the elongation at break thereof is high.
In the extrusion process (normal system for manufacturing the fibers), drawing is subsequently carried out with stretching ratios of between 1:10 and 1:20, the elastic modulus of these types of fibers can thereby be greatly improved, however, it still being insufficient in many cases for providing the features sought. In order to obtain a greater elastic modulus, an attempt can be made to increase the stretching ratio, however, industrial manufacture becomes unstable, many breakages of the thread, which the fibers form, being produced, undesirable deformations of the section of the same, etc. The deterioration which the features of the fibers can suffer may be very high if this stretching is not done in a very rigorous manner and applying complementary treatments.
In order to resolve this drawback, this applicant is the holder of the patent ES2396639A1, in which a “Method for manufacturing structural synthetic fibers for concretes and mortars for increasing the elastic modulus of the same” is disclosed, which considers that after the first stretching process, the threads are subjected to a second stretching phase, in advance of which they are heated so that they are within the softening range and in addition, or alternatively, special nanoclays with nanometric size are added to the polymer, the preferred nanoclays used being sepiolite, with a nanometric size, modified with xylans.
Although said method satisfactorily meets the intended objective, it presents certain aspects capable of being improved, the objective of the present invention being the development of a new improved method for such purpose.